Heat Pumps – How Well Do They Work?
DEAR TIM: I am going to have a heat pump installed in my home. Can these systems really heat a house in cold weather? I am confused about the energy efficiency ratings. Are some heat pumps more efficient than others? Will I save money in the long run by buying the most efficient unit? Is it true that the refrigerant Freon-22 has been outlawed? Dennis S., Oregon City, OR
DEAR DENNIS: Believe it or not there is heat in cool and cold air. Heat pumps can extract this warmth and inject it into your home. They achieve this by doing the same thing air conditioners do only backwards! In hot weather air conditioners, using the magic of special refrigerant chemicals, take heat from the inside of your house and dispose of it outdoors. It only makes sense that the modified machines can do the exact opposite and pull heat from outdoor air and pump it into your home.
Heat pumps work very efficiently when the outdoor temperature is in the 50 F range. As the outdoor temperature drops, the heat loss of a home is greater and the heat pump needs to operate for longer periods of time to maintain a constant indoor temperature. Around 37 F many heat pumps reach what is called the balance point. At or near this temperature the heat pump needs to run constantly to produce enough heat to maintain a comfortable indoor temperature.
As the outdoor temperature continues to drop, the heat pump needs help from traditional electric resistance heat coils. These coils resemble the glowing wires inside your toaster and consume vast amounts of electricity as they burn to keep you warm. Your thermostat will most probably have a light that comes on when this happens. It is usually labeled as emergency or auxiliary heat. If this light is on whenever your heat pump is working, you should have a professional service your system.
Manufacturers can make heat pumps operate at different levels of efficiency. The more heat a system can produce or remove from a given amount of electricity, the more efficient it is. A common measurement of this performance is the Seasonal Energy Efficiency Ratio (SEER). SEER numbers can vary widely if you compare old heat pumps to new ones. Twenty year old heat pumps often had peak SEER numbers of 6. The minimum SEER you can buy today is 10. The highest SEER heat pumps made at present are a tad over SEER 16. Any heat pump that has a SEER rating above 14 is very high efficiency.
The SEER numbers are a little misleading. They actually are a measurement of the efficiency of the heat pump when it is in the cooling or air conditioning mode. If you live in a warm or hot climate, it might make great sense to purchase a heat pump with a high SEER value. People who live in cool or cold climates may not get a payback for the extra money they spend for a high value SEER heat pump. What's more, those who have high electricity costs will save more than those who have access to inexpensive electricity. It can be confusing to say the least.
For example, if your house needs a 3 ton heat pump, your average electric rate is $.0867 per kilowatt-hour, and you live in New England, you might only save $36 per year in cooling costs when you upgrade from a SEER 10 to a SEER 13 heat pump. Your overall savings when you heat and cool for an entire year might only be $189. A person who lives in south Florida who has the exact same system and utility rates could possibly save $173 per year in cooling costs and an overall annual savings of $215 by upgrading from a SEER 10 to 13. Professional heating and cooling contractors can help you estimate savings for your area.
The Environmental Protection Agency, in accordance with the Montreal Protocol, is obligated to phase out over a period of years hydrochloroflourocarbon (HCFC) refrigerants used in heat pump and air conditioning systems. Most residential systems currently use a refrigerant called Freon-22 that happens to be in this group. Starting January 2004, we must begin to scale back the use of Freon-22. In the year 2010, companies are no longer allowed to manufacture equipment that uses Freon-22. In 2020, Freon-22 will not be permitted to be imported or manufactured in the USA.
Since the useful life of most heat pumps is between 10 - 15 years, you should be able to easily obtain refrigerant for a heat pump that uses Freon-22. But, as we approach the year 2010, those people who buy one of the last Freon-22 heat pumps may have to pay a king's ransom to get their heat pumps filled with refrigerant if a leak develops.